The present invention relates generally to a fastener device capable of providing an indication of tension in a fastened joint.
The present invention more particularly relates to an improvement in a tension indicating device wherein a compressible spring washer is utilized in conjunction with a gauge to be clamped between the spring washer and a bearing surface providing a condition which is directly relatable to tension in the joint.
Prior art devices of this general type generally rely upon a particular configuration of a nut or bolt head as the means for clamping the gauge between the nut or bolt head and the spring washer. Quite often, an accurate indication of tension is required in a joint which utilizes a somewhat standard bolt head or nut body configuration. It is often desired to place the tension indicating portion of the fastened joint in the joint at the time of application rather than utilize a device which is preassembled to a nut or bolt member.
Accordingly, it is a general object of the invention to provide a washer unit which is capable of accurately indicating tension in a joint.
It is another object of the invention to provide a tension indicating washer unit which may be utilized with a variety of bolt head styles and/or nut body styles.
Still another object of the invention is to provide a multipiece, preassembled washer unit which is capable of simultaneously providing a spring to a joint and providing an indication of the attainment of a predetermined tension level in the joint. Still another important object of the invention is the provision of a tension indicating washer preassembled unit which is relatively insensitive to the various tolerance ranges which may exist in the manufacture of standard cold headed or formed fasteners, such as nuts or bolts.
These and other objects and advantages are obtained in the present invention in which a multipiece washer unit is comprised of an upper load accepting washer and a lower conical-type spring washer which are joined at their inner peripheral margins and which a ring-type cup-shaped gauge is positioned near the outer peripheral margins of each washer and preassembled therebetween. As a bolt or nut member is torqued, the spring washer will compress, diminishing a gap between the lowermost outer peripheral margin of the upper washer and the upper surface of the spring washer to the point where the gauge is pinched between the surfaces. At this point, the gauge will no longer be free to rotate relative to the washer members, thus providing an indication of the attainment of a predetermined tension level. The preferred embodiment of the preassembled washer unit includes an upper washer having a slight draft or conical shape to insure that load is applied at the inner peripheral margin thereof. A cup gauge member is preferably formed to include upstanding side walls which are corrugated so that they may contact the outer periphery of the upper washer and be laterally sized thereon.
A particular advantage of the structure utilized in the present invention is the ability to serially arrange a plurality of washer units having increasing resistance to compression thereby enabling the user to be consecutively apprised of increasing tension levels in the joint.
The foregoing and other objects and advantages will become more apparent from the following detailed description when considered in conjunction with the accompanying drawings, wherein like reference numerals throughout the various views of the drawings are intended to designate similar elements of the component.